This invention relates in general to weight measuring devices and, more particularly, to an onboard indicator for measuring the weight of a vehicle.
Onboard weight indicators such as shown in U.S. Pat. Nos. 3,648,790, 3,857,093, 3,955,636, and 4,623,029 are used to determine the weight of a load applied to a vehicle. Indicators of this type generally operate by measuring the deflection of the vehicle springs and then correlating the deflection with a known or calculated weight of the vehicle. A transducer is typically used to measure the spring deflection and a signal is then sent from the transducer to a suitable processor unit which calculates and displays the vehicle weight. These types of onboard weight indicators are particularly advantageous because they allow the vehicle load to be determined while the vehicle is being loaded and without requiring that the vehicle be positioned on a stationary scale.
Many of these conventional types of conventional onboard weight indicators are mounted at opposite ends of each axle on the vehicle. Because of the costs associated with the transducers or other weight sensing portions of the weight indicators, a weight indicator was disclosed in U.S. Pat. No. 4,789,033 which allows a single transducer to be mounted between the tandem axles of a vehicle. This mounting arrangement allows the single transducer to be used to measure the load applied to a set of tandem axles. As a result, significant cost savings can be achieved in comparison to other weighing systems which require that a weight indicator be positioned at each end of every axle on the vehicle.
When using a single weight indicator to measure the deflection of tandem axles, it is important that the transducer be vertically oriented at a central position between the axles. When positioned in this manner, the transducer functions like a fulcrum and more accurately averages the movement experienced by both axles. Similarly, when one indicator is used on a single axle, the associated transducer should be centrally positioned between the ends of the axle to average the load applied to the axle. Often, however, the drive train or components of the vehicle frame interfere with the desired positioning of the transducer on tandem and single axle vehicles. The transducer must then be positioned off-center, with resulting inaccuracies in the measurement of a load applied to the axles. A need has thus arisen for an onboard weight indicator which allows a single transducer to be mounted off-center and still maintain a more accurate averaging of the load applied to a single or tandem axle.